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Forum: Processes Involving Optical Photons
Re: None Optical photons and Shashlik calorimeter (Alessandro Berra)
Date: 09 Nov, 2015
From: Gumplinger Peter <Gumplinger Peter>

Hi Alessandro,

> 1) The scintillator tiles have a polished surface and will be painted
> with a reflective white paint, thus I think I have to define an array of
> "polishedfrontpainted" G4LogicalBorder surfaces between the physical
> volumes of the scintillating and absorbing tiles. Is it correct?

Yes, but it is easier if you defined just one G4LogicalSkinSurface ("polishedfrontpainted") for the absorbing tile. Any optical photon wanting to leave into an absorbing tile will see this surface ... though this now includes the situations where a photon hits the absorbing tile in the WLS fiber hole. But this can also be 'overwritten'. The presidence in the code is the following:

        Surface = G4LogicalBorderSurface::GetSurface(thePrePV, thePostPV);

        if (Surface == NULL){
          G4bool enteredDaughter= (thePostPV->GetMotherLogical() ==
                                   thePrePV ->GetLogicalVolume());
            Surface =
            if(Surface == NULL)
              Surface =
          else {
            Surface =
            if(Surface == NULL)
              Surface =
                G4LogicalSkinSurface::GetSurface(thePostPV->GetLogicalVolume());          }

e.g. If a G4LogicalBorderSurface is found between the two G4VPhysicalVolumes it takes presidence. If not, then it depends on wheter or not a daughter volume of the parent is intered. If not, a PreStep-LogicalSkinSuface is used if it existes, else the PostStep-LogicalSkinSurface is used. If a daughter is entered, the PostStep-LogicalSkinSurface takes presidence over the PreStep-LogicalSkinSurface. So, the absorbing tile's LogicalSkinSurface is not used if the WLS-hole also has a LogicalSkinSurface and is a daughter volume of the absorbing tile. (e.g. it's not entering a daughter but leaving a daughter).

> 2) The 5mm thickness of each scintillating tile is facing the world
> volume, thus I need to define another array of "polishedfrontpainted"
> G4LogicalBorder surface between the scintillating tile and the physical
> World Volume. Is it correct (again)?

Yes, but again, you can use the trick with the "ordered presidence skin surfaces". You can give the World Volume a skin surface!

> 3) All the tiles (iron and scintillating ones) will be mechanically
> drilled to create the holes to insert the WLS fibers. The holes will be
> 0.1mm larger than the fiber and no optical grease will be used to fill
> the holes, thus an air gap will be present. Thus, I think I have to
> define many G4LogicalBorder surfaces (one for each hole) with "ground"
> finish between the scintillator tile and the hole physical volumes. Is
> it correct?

Well, better to give the air hole a "ground" skin surface. (you can't give the scintillating tile a skin-surface because the surface with the world is different to the surface with the WLS-hole.)

> If this is the case, the problem is that I don't know a
> reasonable value of the parameters for this surface: sigma_alpha,
> specular lobe constant and so on.

You can give your best estimate and/or play with different parameters to see the difference it makes to your result.

Hope this helps, Peter

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1 None: Re: Optical photons and Shashlik calorimeter   (Alessandro Berra - 10 Nov, 2015)
(_ Feedback: Re: Optical photons and Shashlik calorimeter   (Gumplinger Peter - 10 Nov, 2015)
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